FAQ on CDSL:
FREQUENTLY ASKED QUESTIONS ABOUT ROCKWELL'S CONSUMER DIGITAL
SUBSCRIBER LINE (CDSL) TECHNOLOGY
October 1997
1. What is Consumer DSLT technology?
A: Consumer Digital Subscriber Line (CDSL or Consumer DSL) technology is another exciting new modem technique
in Rockwell's growing family of personal communications electronics technologies. It is a 1Mbps digital modem
technology that matches earlier conventional analog modem technology in price and simplicity. CDSL modems will be
priced, sold and installed much like today's popular V.34 and K56flex modems, yet will offer downstream data transfer
speeds 10 to 20 times faster. Designed with the consumer in mind, CDSL modems will offer an affordable 1Mbps
solution for consumer Web browsing and remote computing over standard copper telephone lines.
Rockwell believes CDSL represents the next logical step after K56flex modems, and has elected to unveil the
technology early in the standards development process in order to solicit the broadest possible industry participation
among the companies who must collectively define an interoperability standard for it. The International
Telecommunications Union (ITU) Study Group 15 is now focusing on a new category for this type of technology called
G.adsl lite.
2. How does CDSL technology compare to 56Kbps modems?
A: CDSL technology will offer speeds from 10 to 20 times faster than 56Kbps modems, yet use the same easy
deployment model. An added benefit is that it can operate simultaneously with Plain Old Telephone Service (POTS) for
voice calls, and CDSL service can be "always connected" like a LAN connection. This would never be possible with
conventional analog modems like 56Kbps products, because 56Kbps modems connect through the telephone companies'
voice switches before being connected to the ISP over a digital T1/E1 line. Linking through the switch puts a ceiling on
performance and restricts the line to a single operation at a time.
In contrast, CDSL modems will connect directly to a separate high-speed digital network that the telephone companies
can easily provision using head-end CDSL technology. The CDSL modems can be used to make an Internet connection at
the same time the line is being used to make a voice call.
3. Will CDSL replace K56flex modems?
A: CDSL will take some time to standardize and deploy. Additionally, even then, CDSL technology requires special
provisioning at the central office. For mobile users, this special provisioning may not be available. For these users,
K56flex will still be the right choice. CDSL modems will continue to include all industry standard modem modulations,
including K56flex and V.34.
4. I thought 56Kbps was the highest modem speed you can get over standard telephone lines.
A: It is, when you're limited to the 4 Khz POTS bandwidth. However, since CDSL modems bypass the voice switches,
they're able to use much more bandwidth on the local copper loop. The use of this additional bandwidth makes the
higher speed possible. And by using innovative techniques to enable CDSL and POTS to co-exist on the same line
without interfering with one another, CDSL service can be installed without the need for special wiring or equipment,
providing the consumer with a much more flexible, multi-service solution on a single phone line.
5. Will I be able to upgrade my K56flex modem to CDSL?
A: It will not be possible to do a software upgrade of a K56flex modem to CDSL since the bandwidth is much greater.
The analog interface components, including the line transformer and codec, are very different.
6. What are the benefits of CDSL technology for mainstream PC consumers?
A: CDSL technology offers a number of benefits: (1) significantly faster download speeds (from 10 to 20 times faster
than conventional modems); (2) deployment using the same straightforward model as traditional analog modems; (3)
simultaneous operation with Plain Old Telephone Service (POTS) for voice calls; and (4) low cost, enabling retail
products at traditional modem price points that also include industry standard modulations such as K56flex, V.34,
V.32bis, and fax modulations.
7. Will CDSL vary in performance depending on line length and conditions, as do K56flex modems?
A: CDSL is indeed dependent upon line length and conditions, as well as on other line dynamics including noise and
crosstalk. However, the techniques developed by Rockwell engineers will maximize CDSL performance in most
environments.
8. How does CDSL technology compare with Discrete Multi-Tone (DMT) or Carrierless Amplitude and Phase (CAP)
ADSL technology?
A: CDSL technology is similar to but operates at a lower rate than DMT or CAP ADSL technology. With its 1Mbps
downstream data rate, CDSL is much more cost-effective to implement than DMT or CAP ADSL modems, and its speed
is ideal for Web browsing and remote computing. Also, CDSL technology eliminates the need for "splitters" that the
phone company previously had to install at the subscriber's home to separate the phone service frequencies from
traditional ADSL frequencies. Instead, special techniques allow CDSL to resolve the noise interference problems that
existed between traditional ADSL technology and POTS service so that the two can co-exist on the same line. This
allows a dual-operation capability -- CDSL can maintain a continuous link to the phone company just like a LAN
connection, and the user can make a phone call simultaneous with an Internet connection on the same standard phone
line.
9. How is ADSL technology normally deployed?
A: Existing ADSL techniques require that the phone company install a splitter in the subscriber's home to separate the
Plain Old Telephone Service (POTS) frequencies from the ADSL frequencies. Additionally, wire must be run from the
splitter to the location where the ADSL modem will be installed, unless a second pair of lines is already installed and
can used for this connection. The phone company provides all of the labor and materials for this installation, and also
must provide the modem to the subscriber, making for an expensive and inconvenient deployment model.
10. What is different about CDSL deployment as compared to traditional ADSL deployment?
A: The key difference from a deployment perspective is that CDSL technology does not require the installation of a
splitter in the home to separate the CDSL frequencies from the POTS frequencies. The consumer can simply buy a CDSL
modem at the same place where conventional analog modems are purchased, and plug it into the telephone jack.
11. Will CDSL replace standard ADSL technology?
A: No. In order for CDSL to operate on the same line as the POTS telephone service without a splitter, it must run at a
slower rate than existing ADSL technologies. Standard ADSL will allow the telephone companies to provision the
highest data rate service possible, serving an important segment of the market.
12. Where does CDSL fit in Rockwell's overall DSL plans? How does it compare to another previously announced
Rockwell DSL product called ZipWire?
A: CDSL is a key member of a growing family of DSL products and technologies. Through its September 1996
acquisition of Brooktree Corp., Rockwell has been a pioneer in industry-standard High Bit Rate Digital Subscriber Line
(HDSL) technology that is now used to provision the overwhelming majority of the world's digital T1/E1 connections.
In 1996 and 1997, Rockwell introduced the first members of its ZipWire family of mid-rate DSL solutions for business
connectivity applications and for low-cost T1/E1 provisioning and mult-service "pairgain" voice/data/fax applications
in emerging countries. Together, this growing family of DSL products leverages Rockwell's long-time modem expertise
in core digital signal processing and signal conversion technologies to take modem connectivity into the next decade and
beyond
13. How is CDSL technology provisioned at the central telephone office?
A: Rockwell is working closely with the telephone companies to develop provisioning models for CDSL. To activate
CDSL service, local exchange carriers (the telephone companies) will simply install CDSL equipment in their central
offices for those customers who choose to take the service. A high-speed ATM or frame relay data network will likely
be used to tie the central offices together. Internet Service Providers (ISPs) will gain access to customers by connecting
to this high-speed network.
There are two models for equipment installation at the central office. One model embeds CDSL technology into Digital
Subscriber Line Access Multiplexer (DSLAM) equipment, a type of equipment that was specified by the regional Bells'
Joint Procurement Consortium as a method for combining a variety of subscriber services into a single multi-service
solution. A second model will allow telephone companies to offer CDSL technology at even lower cost, by embedding
CDSL technology in line cards for switches and DLC equipment. To do this, Rockwell will provide very low power
chipsets for CDSL.
14. Will there be any tariffing issues involved before telephone companies can provision CDSL service?
A: No serious problems are expected. Many of the telephone companies are already offering ADSL services, mostly as
a regulated offering. With the experience the telephone companies have with ADSL, It should be fairly easy for them to
offer Consumer DSL
15. How interested do the telephone companies seem to be in offering CDSL service?
A: Most have expressed strong interest. The installation cost of ADSL (or as the telephone companies call it, the "truck
roll") has been one of the most serious impediments to a widespread rollout. Consumer DSL will allow the telephone
companies to offer ADSL services within the consumer's "willingness to pay" range. Additionally, Consumer DSL will
allow the telephone companies to "tier" their service offerings by providing a lower speed, lower cost service with an
upgrade to a higher speed, higher cost service.
16. How does CDSL technology compare to cable modems?
A: Rockwell also has development programs underway for cable modems, and sees an exciting future for them. Cable
modems have the potential to offer significantly higher data rates than CDSL, but they have a number of deployment
issues. Operating two-way data service over a cable plant requires a significant upgrade to entertainment-grade cable
systems. Additionally, cable data service is less secure since all data flows to all houses. Finally, real standards for
cable modems are just being rolled out and users cannot purchase cable modems in retail channels yet.
Cable modems, however, show great promise and will likely co-exist with ADSL as alternative ways for consumers to
gain high-speed access.
17. How will a consumer know whether he is a good candidate for CDSL service?
A: Anyone who does a significant amount of remote computing or needs high-speed Internet connections is a candidate
for CDSL service. However, the user must fall within the "ADSL serving area" for the telephone company to provide
this access. In general, this means that the consumer's local loop does not exceed 18,000 feet.
18. When can users expect to see CDSL service?
A: The telephone companies will trial this technology for at least six months before beginning to rollout the service.
Additionally, the telephone companies will not roll out a service unless the technology is a standard, or is supported by
the majority of the industry. The earliest potential availability of this service is likely to be late 1998.
19. How will users sign up for CDSL service?
A: If the consumer's telephone company offers the CDSL access, the user will most likely sign up for access with the
local telephone company. Payment will, of course, simply appear on the user's telephone bill. It is likely that the
telephone company will offer CDSL access as a regulated service, which means that they will have to provide a
mechanism for Internet Service Providers to gain access to the data network which CDSL is a part of. The most likely
way to do this is for the telephone company to provide an ATM or frame relay network which connects all of the central
offices together. Internet Service Providers will, then, be given access to this ATM network so they can provide service
to the user.
If the telephone company offers Internet Service, it is likely to be as an unregulated service.
20. How much will monthly fees be for CDSL service?
A: It is impossible to predict what the telephone companies will charge for CDSL service. However, a number of
industry analysts believe the consumer willingness to pay for both data access and Internet access is about $40-45 per
month.
21. Where will users buy CDSL modems, and what are they likely to cost?
A: Consumers will be able to buy CDSL modems at the same places where they buy conventional analog modems, and
they are likely to have the same retail price points, starting at approximately $200 for first-generation products. Prices
will decline as the market matures, most likely at the same rate that the prices of other analog modem products have
declined.
Additionally, just as traditional analog modems have been provided with personal computers (PCs), it is likely that PC
manufacturers will begin offering CDSL modems with their PCs.
22. Are standards required for CDSL modems?
A: Yes. Standards will be critical to ensure a wide variety of retail modem products that can be interoperable with
head-end equipment at the central office. The same standards bodies that developed and ratified global standards for
conventional analog modems will do the same for 1Mbps digital modems. Earlier this year, Study Group 15 of the
International Telecommunications Union (ITU) opened a new standards category called G.adsl lite. Although the terms
of reference for this category have not yet been established, they are likely to be similar to the design principles of
CDSL.
23. What is Rockwell doing to support CDSL modem standards?
A: Rockwell will support the work in the ITU Study Group 15 to establish standards for this technology, and has
announced CDSL technology early in the standards development cycle as a first step in this process. Rockwell will also
collaborate with other industry leaders in the appropriate forums and standards bodies to standardize this technology.
24. Will Rockwell license the specification for Consumer DSL to other companies in the industry?
A: Rockwell will license the specification for Consumer DSL to other companies in a manner similar to the way we
licensed the specification for K56flex. Through this licensing program, K56flex has become the most widely supported
technology for 56Kbps in the world.
25. Will there be another "modem war" over CDSL technology?
A: We certainly hope not. The best scenario for consumers, product manufacturers and the market as a whole is for the
industry to rapidly develop global interoperability standards for this exciting new technology.
26. Will CDSL performance be limited by FCC restrictions, as K56flex modem performance is?
A: No, CDSL operates within the ADSL power specifications established in ANSI T1E1.413.
27. Will there be field trials for CDSL service, similar to those that have been conducted for standard ADSL service?
A: Absolutely. A number of telephone companies have volunteered to host trials of CDSL. Rockwell will finalize plans
for trials early in 1998.
28. What will ISPs have to do to provide CDSL service?
A: In general, ISPs will not provide CDSL service directly. The CDSL access will be provided by the local telephone
companies and Competitive Local Exchange Carriers (CLECs). The entity which provided the CDSL access will
provide the ISP with access to its data network. In this way, the ISP will gain access to the user.
29. When will Rockwell make CDSL chip sets available?
A: Rockwell expects to begin shipping CDSL chip sets to modem manufacturers in the spring of 1998.
30. There seem to be so many modem technologies available today, from K56flex modems to cable, DSL and even
satellite set-top box devices. How does a consumer decide what's right for him?
A: Rockwell believes that users will have a growing variety of personal communications options for Internet
connectivity and remote computing. The right choice will depend on where you live, what your local providers are
offering and what you need. It's important to understand that the underlying technology for all of the options is very
similar. Rockwell has developed a set of core digital signal processing and mixed-signal semiconductor technologies
specifically for high-speed communications, and this expertise allows us to quickly develop products across all of these
categories. We believe that the user's options will only get broader as time goes by, and we intend to support customers
with as many of these options as possible and provide the broadest portfolio of semiconductor system solutions for
personal communications electronics. |
